Islamic State propagandists are seeking to capitalize on last week's terror attack in London, which left five people dead and 40 injured, by flooding YouTube with hundreds of violent recruitment videos.
The online propaganda offensive comes as Britain demands social media companies scrub their sites of jihadist postings.
Amber Rudd, the country's interior minister, has vowed to "call time" on internet firms allowing terrorists "a place to hide" and has summoned some of the leading social media companies, including Facebook and Twitter, for what is being dubbed by British officials as "showdown talks" later this week.
Rudd says she is determined to stop extremists "using social media as their platform" for recruitment and for operational needs.
Britain's security services are in a standoff with WhatsApp, which has refused to allow them access to the encrypted message the London attacker sent three minutes before he used an SUV to mow down pedestrians on Westminster Bridge and stabbed to death a policeman outside the House of Commons.
British security services are powerless to read that final message, which might cast light on whether the attack was a "lone wolf" or one aided and directed by others. Police investigators believe the terrorist acted alone and have seen no evidence that he was associated with IS or al-Qaida.
WhatsApp, which has a billion users worldwide, employs "end to end encryption" for messages, which the company says prevents even its own technicians from reading people's messages.
Officials want voluntary action
Rudd and other government ministers have launched a media onslaught, saying they are considering legislation to require online companies to take down extremist material. They argue this wouldn't be necessary if the companies recognized their community responsibilities.
Rudd told the BBC that Facebook, Google and other companies should understand they are not just technology businesses, but also publishing platforms. "We have to have a situation where we can have our security services get into the terrorists' communications," she argued. "There should be no place for terrorists to hide."
British Foreign Minister Boris Johnson joined in the condemnation of social media and online companies. "I think it's disgusting," he told The Sunday Times. "They need to stop just making money out of prurient violent material."
At a security conference last week in the United States, Johnson called for action.
"We are going to have to engage not just militarily, but also to stop the stuff on the internet that is corrupting and polluting so many people," he said. "This is something that the internet companies and social media companies need to think about. They need to do more to take that stuff off their media — the incitements, the information about how to become a terrorist, the radicalizing sermons and messages. That needs to come down."
The furor over extremist use of the internet was fueled Monday by front-page articles in the Times and Daily Mail newspapers highlighting the IS propaganda videos posted on YouTube since last Wednesday's slaughter in the British capital. The high-definition videos, some of which contained references to the London attack, include gory scenes of beheadings and "caliphate violence" carried out by child adherents of the terror group.
U.S. and European officials have long complained online companies are, in effect, aiding and abetting terrorism. A year ago in January, much of the U.S. national security leadership of the Obama administration sat down with Silicon Valley chiefs to discuss jihadist use of the internet to recruit and radicalize people and plot attacks.
Also last year, British spy chief, Robert Hannigan, singled out messaging apps as especially worrisome for the security services, saying they had become "the command-and-control networks of choice for terrorists and criminals — precisely because they are highly encrypted."
After initial resistance to complaints from Western governments, Facebook, Google and Twitter have in recent months been more cooperative with authorities and have removed large amounts of extremist material. Twitter said in the second half of 2016 it suspended 376,890 accounts for violations related to promotion of terrorism.
But some services have resisted providing governments with encryption keys, or so-called back doors.
Apple has developed encryption keys that message users can use that are not possessed by the company. Apple's chief executive, Timothy Cook, argued last year, "If you put a key under the mat for the cops, a burglar can find it, too."
Silicon Valley chiefs say they fear violations of privacy and their priority is their customers, not national security, an argument that has resonated since former U.S. National Security Agency contractor Edward Snowden revealed the extent of electronic surveillance by U.S. intelligence agencies.
Last year, WhatsApp was blocked several times in Brazil for failing to hand over information relating to criminal investigations.
Messages sent on a rival service by Telegram are also encrypted, but after bad publicity and immense pressure from Western governments, the company does provide a backdoor for security and law-enforcement agencies.
Not that access to encrypted communications always helps.
Sunday, it emerged that German police knew the Christmas market attacker in Berlin who drove a truck into a crowd of shoppers was planning a suicide attack. Police had intercepted his Telegram messages nine months before the attack.
A police recommendation that he be deported was declined by state government prosecutors because they feared the courts would reject the request.